Structural rearrangements in hairy-rod polymer solutions undergoing shear

• Published in: Rheologica acta Vol. 38; no. 6; pp. 514 - 527
• Main Authors: Hilliou, Loic, Vlassopoulos, Dimitris, Rehahn, Matthias
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Berlin Springer 01.12.1999; Springer Nature B.V
• Subjects: Anisotropy; Applied sciences; Birefringence; Breakup; Clusters; Deformation; Dilution; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Polymers; Properties and characterization; Shear; Size distribution; Solution and gel properties; Time dependence; Vorticity; Conjugated polymer; Chemical solution; Phenylene derivative polymer; Shear flow; Concentration effect; Aromatic polymer; Temperature effect; Molecular rearrangement; Molecular aggregation; Experimental study; Comb polymer
• ISSN: 0035-4511; 1435-1528
• DOI: 10.1007/s003970050204

We report on a rheooptical investigation of hairy-rod poly(p-phenylene) solutions at different concentrations and temperatures. These polymers have a reasonably high persistence length (about 28 nm) and behave as worm-like chains in dilute solutions, whereas they form nearly spherical fractal aggregates with internal anisotropy at higher concentrations. By exposing these systems to time-dependent simple shear and following the evolution of birefringence in start-up and its subsequent relaxation upon the cessation of shear, we find a substantial broadening of the cluster size distribution, resulting from flow-induced cluster deformation and break-up. In contrast to the very dilute solutions, where polymers align in the flow direction, the deformed clusters main axes are aligned in the vorticity direction, presumably due to their strong steric local pretransitional type of ordering, with the constituent polymers following the velocity vector. At the highest concentration, which corresponds to a weak gel, shear is shown to break-up the gel and the steady-state response of a broad-size aggregate suspension is eventually recovered.